Faculty Bibliography

Purpose/UNASSIGNED:While Ir-192 remains the mainstay isotope for gynecologic high-dose-rate (HDR) brachytherapy in the U.S., Co-60 is used abroad. Co-60 has a longer half-life than Ir-192, which may lead to long-term cost savings; however, its higher energy requires greater shielding. This study analyzes Co-60 acceptability based on a one-time expense of additional shielding and reports the financial experience of Co-60 in Peru's National Cancer Institute, which uses both isotopes. Material and methods/UNASSIGNED:A nationwide survey was undertaken assessing physician knowledge of Co-60 and willingness-to-pay (WTP) for additional shielding, assuming a source more cost-effective than Ir-192 was available. With 440 respondents, 280 clinicians were decision-makers and provided WTPs, with results previously reported. After completing a shielding report, we estimated costs for shielding expansion, noting acceptability to decision makers' WTP. Using activity-based costing, we note the Peruvian fiscal experience. Results/UNASSIGNED:Shielding estimates ranged from $173,000 to $418,000. The percentage of respondents accepting high-density modular or lead shielding (for union and non-union settings) were 17.5%, 11.4%, 3.9%, and 3.2%, respectively. Shielding acceptance was associated with greater number of radiation oncologists in a respondent's department but not time in practice or the American Brachytherapy Society membership. Peru's experience noted cost savings with Co-60 of $52,400 annually. Conclusions/UNASSIGNED:By comparing the cost of additional shielding for a sample institution's HDR suite with radiation oncologists' WTP, this multi-institutional collaboration noted < 20% of clinicians would accept additional shielding. Despite low acceptability in the US, Co-60 demonstrates cost-favorability in Peru and may similarly in other locations.

Purpose: While Ir-192 remains the American mainstay isotope for gynecologic high dose rate (HDR) brachytherapy, Co-60 is an isotope that has been used abroad but has yet to impact the U.S. market. Co-60 has an advantage of a longer half-life than Ir-192 which may lead to long-term cost-savings; however, its higher energy requires greater shielding than does Ir-192. To assess clinicians' acceptability for this one-time shielding cost, a survey of U.S. radiation oncologists was conducted, and we previously reported their willingness-to-pay (WTP). The purpose of this study is to analyze what percentage of physicians would accept the onetime expense of additional shielding based on cost estimates from an internal shielding report and vendor price quotes for a single sample institution. Materials and Methods: A nationwide survey was undertaken to assess physician knowledge of Co-60 and their WTP a one-time expense for additional shielding, assuming a source more cost-effective than Ir-192 were available. With 440 respondents, 280 clinicians were decisionmakers who provided WTP answers, and the results were previously reported. Subsequently, we conducted shielding analysis of an HDR suite in a single sample institution to obtain the tenth-value layers (TVLs) necessary to maintain adequate shielding. Partnering with an external vendor of both lead and ultra-high density modular shielding, we calculated the costs necessary for design, shielding, shipping, and installation for both union and non-union settings, and compared these costs to decision makers' WTP. Results: For the single institution sample suite to appropriately shield for Co-60, 1.11 TVLs, 2.46 TVLs, and 1.15 TVLs would have to be added, respectively, to the walls, door, ceiling & floor to achieve the same current level of shielding. Cost estimates of adding shielding using proprietary ultra-high density modular shielding were $173.5K and $211K for non-union and union setting, respectively. Costs for lead shielding instead were $376.5K and $418K, respectively. The percentage of all 280 respondents who would accept these cost estimates for ultrahigh density modular shielding (union and non-union) or lead shielding (union and non-union) were 17.5%, 11.4%, 3.9%, and 3.2%, respectively. Of the 122 self-described decision-makers who were ABS members, the percentage of these who would accept these cost estimates for ultra-high density modular shielding (union and non-union) or lead shielding (union and non-union) were 18%, 9%, 2.4%, and 1.6%, respectively. of the 227 self-described decision-makers who were more than 5 years postresidency completion, the percentage of these who would accept these cost estimates for ultra-high density modular shielding (union and nonunion) or lead shielding (union and non-union) were 18.5%, 12.8%, 4.4%, and 3.5%, respectively. Conclusions: By comparing the cost of additional shielding for a sample institution's HDR suite with radiation oncologists' WTP, this multiinstitutional collaboration noted that less than 20% of clinicians would accept the most favorable financial situation of ultra-high density modular shielding with non-union labor. Percentage of cost-acceptability did not vary in subgroup analysis by ABS membership or years of experience. This analysis is limited by looking at the TVL requirements of only a single sample institution and cost estimates from a single vendor. However, knowing that the sole vendor of Co-60 afterloaders for gynecological cancer brachytherapy treatment has left the American market, we gain information by looking at the cost of shielding with reference to clinician WTP

Purpose: Recently the Gamma Index of registered CBCT and CT, combining mass density and distance-to-agreement (DTA), has been used as an effective means to evaluate the quality of image guided pretreatment setup, and to identify radiation-induced patient anatomy change. The pass/fail of the Gamma analysis relies heavily on the Gamma criteria. We propose a regression model based on multiple patient data to quantitatively determine the optimal HU and DTA criteria for CBCT Gamma analysis. Methods: We retrospectively analyzed daily setup kV-CBCT (acquired using OBI on True- Beam, Varian Medical) from 10 H&N, 10 thoracic, and 10 abdominal cancer patients. The registration between CBCT and the planning CTwas conducted online by therapists and reviewed by radiation oncologist. Visible region of interests were contoured in the CBCT by experts as the ground truth of CT/ CBCT similarity. Gamma analyses using different levels of criteria, combinations of mass density 0.2 g/cc, 01 g/cc, and 0.05 g/cc, and DTA 3 mm, 2 mm, and 1 mm, were repeated on CBCT using the MobiusCB (by Mobius Medical System) software. The Gamma passing rate of the total irradiated volume and selected region of interests at different levels of gamma criteria were used as training data for multi-variated parametric regression model to determine the optimal gamma criteria. Results: Based on the preliminary data, the optimal Gamma criteria is 0.5 g/cc and 3 mm for head&neck patients, 0.2 g/cc and 2 mm for thoracic cancer patients, and 0.1 g/cc and 2 mm for abdominal cancer patients, depending on clinically used setup margins. Conclusion: Gamma Index of the target volume should be used for CBCT gamma analysis. For different part of the body the optimal CBCT Gamma criteria varies. By using the optimal Gamma criteria, we expect the 90% and 85% Gamma passing rate which are the accepting and warning threshold respectively can be used to accurately guide clinical decisions

PURPOSE/OBJECTIVE:Through-plane motion introduces uncertainty in 3D motion monitoring when using single slice on board imaging (OBI) modalities such as cine MRI. We propose a principal component analysis (PCA) based framework to determine the optimal imaging plane to minimize the through-plane motion for single slice imaging based motion monitoring METHODS: Four-dimensional computed tomography (4DCT) images of 8 thoracic cancer patients were retrospectively analyzed. The target volumes were manually delineated at different respiratory phases of 4DCT. We performed automated image registration to establish the 4D respiratory target motion trajectories for all patients. PCA was conducted using the motion information to define the three principal components of the respiratory motion trajectories. Two imaging planes were determined perpendicular to the second and third principal component respectively to avoid imaging with the primary principal component of the through-plane motion. Single slice images were reconstructed from 4DCT in the PCA-derived orthogonal imaging planes, and were compared against the traditional AP/Lateral image pairs on through-plane motion, residual error in motion monitoring, absolute motion amplitude error, and the similarity between target segmentations at different phases. We evaluated the significance of the proposed motion monitoring improvement using paired t-test analysis. RESULTS:The PCA-determined imaging planes had overall less through-plane motion compared against the AP/Lateral image pairs. For all patients, the average through-plane motion was 3.6 mm (range: 1.6-5.6 mm) for the AP view, and 1.7 mm (range: 0.6-2.7 mm) for the lateral view. With PCA optimization, the average through-plane motion was 2.5 mm (range: 1.3-3.9 mm) and 0.6 mm (range: 0.2-1.5 mm) for the two imaging planes respectively. The absolute residual error of the reconstructed max-exhale-to-inhale motion averaged 0.7 mm (range: 0.4-1.3 mm, 95% CI: 0.4-1.1 mm) using optimized imaging planes, averaged 0.5 mm (range: 0.3-1.0 mm, 95% CI: 0.2-0.8 mm) using an imaging plane perpendicular to the minimal motion component only, and averaged 1.3 mm (range: 0.4-2.8 mm, 95% CI: 0.4-2.3 mm) in AP/Lat orthogonal image pairs. The root mean square error of reconstructed displacement was 0.8 mm for optimized imaging planes, 0.6 mm for imaging plane perpendicular to the minimal motion component only, and 1.6 mm for AP/Lat orthogonal image pairs. When using the optimized imaging planes for motion monitoring, there was no significant absolute amplitude error of the reconstructed motion (p=0.0988), while AP/Lat images had significant error (p=0.0097) with a paired t-test. The average surface distance (ASD) between overlaid 2D tumor segmentation at end-of-inhale and end-of-exhale for all eight patients was 0.6±0.2 mm in optimized imaging planes and 1.4±0.8 mm in AP/Lat images. The Dice similarity coefficient (DSC) between overlaid 2D tumor segmentation at end-of-inhale and end-of-exhale for all eight patients was 0.96±0.03 in optimized imaging planes and 0.89±0.05 in AP/Lat images. Both ASD (p=0.034) and DSC (p=0.022) were significantly improved in the optimized imaging planes. CONCLUSIONS:Motion monitoring using imaging planes determined by the proposed PCA-based framework had significantly improved performance. Single slice image based motion tracking can be used for clinical implementations such as MR Image Guided Radiation Therapy (MR-IGRT).

Purpose: Nuclear medicine imaging tests frequently require use of multiple hollow spheres of various size filled with radioactivity in order to measure resolution, contrast, and recovery coefficient. Certain vendor tests can require scans using identical spheres, requiring purchase of multiple sphere sets or specific spheres. Additionally, once filled for testing, spheres become unavailable for other scanners. Therefore, this work sets out to develop 3D printed, fillable spheres for resolution and contrast quality assurance tests of PET and SPECT scanners as customizable, disposable, and low-cost alternatives to those available on the market. Methods: Hollow sphere sets were designed in 123D (Autodesk) with various stem and wall thickness configurations for inner diameter spheres of 5.0, 7.5, and 10 mm. Each sphere and stem were combined and printed as one piece with -20 threads and hollow inner diameter for filling. Spheres were 3D printed using a Makerbot Replicator 2 (Makerbot Industries) using a variety of layer thicknesses, infill and outer shells. All spheres were vacuum tested and leak tested using blue dye in a water bath. Results: The optimal 3D printing parameters were found to be 0.1 mm layer thickness, 100% infill, 1 shell, and transparent filament. Wall thicknesses were successfully reduced to as small as 1 mm while maintaining seal. Spheres printed in 30-45 min for less than $1. MicroCT of each sphere demonstrated that sphere inner diameter was reproducible to within 0.2 mm of the desired diameter. Spheres successfully performed as well as marketed products in PET and cardiac SPECT QA testing. Conclusion: 3D printing of hollow spheres can be an alternative to perform regulatory quality assurance tests on nuclear medicine SPECT and PET cameras. Printed spheres are inexpensive, quick to manufacture, disposable, and configurable for on-demand testing requirements